Endoluminal prostheses are typically used to repair, replace, or otherwise correct a diseased or damaged blood vessel. An artery or vein may be diseased in a variety of ways. The prosthesis may therefore be used to prevent or treat a wide variety of defects such as stenosis of the vessel, thrombosis, occlusion, or an aneurysm and dissections.
One type of endoluminal prosthesis used in treatment and repair of diseases in various blood vessels is a stent. A stent is a generally longitudinal tubular device which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. Endovascular stents have become widely used for the treatment of stenosis, strictures, and aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel.
Stents are generally open ended and are radially expandable between a generally unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded insertion diameter. Stents are often flexible in configuration, which allows them to be inserted through and conform to tortuous pathways in the blood vessel. The stent is generally inserted in a radially compressed state and expanded either through a self-expanding mechanism, or through the use of balloon catheters.
A graft is another type of endoluminal prosthesis which is used to repair and replace various body vessels. Whereas a stent provides structural support to hold a damaged vessel open, a graft provides an artificial lumen through which blood may flow. Grafts are tubular devices which may be formed of a variety of materials, including textile and non-textile materials. Grafts also generally have an unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded diameter. The graft is sutured to the lumen to secure it in place.
It is also known to use both a stent and a graft to provide additional support for blood flow through weakened sections of a blood vessel. In endovascular applications the use of a stent and a graft in combination is becoming increasingly important because the combination not only effectively allows the passage of blood therethrough, but also ensures the implant will remain open. The use of a both a stent and a graft is available in various forms, such as a stent/graft composite or a multi-stage stent/graft where the stent secures the graft in place by pinning it between the stent and the vascular wall. Such stent/graft composite prosthesis are described in U.S. Pat. No. 5,578,071 to Parodi, and U.S. Pat. No. 6,162,246 to Barone.
It is also known to provide delivery systems for delivering such prostheses intraluminally. These standard delivery systems generally include catheters with the prosthesis removably mounted to the distal end of the catheter. Quite often a catheter, introducer sheath, or other similar retaining means is disposed over the prosthesis to removably support the prosthesis on the catheter. Once the prosthesis is situated in the target site in the lumen, the catheter is removed by pulling the sheath or retaining means away from the prosthesis to allow the expansion.
The delivery systems for the multi-stage stent/grafts are more complex because the different expansion properties between the graft and the stent, and the frictional relationship between the two in the sheath. In certain situations irregular expansion of the graft may occur, provoking folds on the graft that act as constrictor rings to limit the expansion of the stent. Moreover, prosthesis employing self-expanding stents typically experience longitudinal lengthening when compressed inside the sheath. When liberated inside the vascular lumen, they radially expand and longitudinally reduce. This change in shape poses a problem when a graft covers the outside of the stent because the grafts tend to deform due to the force exerted on the graft by the moving stent. Therefore multiple deployment systems are used when delivering one then one stent or graft.
Procedural success of the deployment of the stent/graft and the function of the stent/graft require accuracy of deployment and ability to reposition. Accuracy is affected by the environment of deployment being a continuous blood-flow, the location of the procedure in the vascular system, and the design of the stent/graft prosthesis and deployment device. For example, pressure from the high volume of blood flow, especially in the thoracic aorta, must be overcome by the delivery device in order to locate the site of deployment and accurately set the stent/graft prosthesis. The location of deployment adds to the difficulty of placement if, for example, a stent/graft prosthesis is used as an interventional repair of a thoracic aortic aneurysm. A thoracic aortic aneurysm has the added complications of large amounts of blood flowing through this aorta, and the multiple outlet arteries disposing blood thereof. Procedural success requires deploying the stent/graft such that the proximal and distal sections of the device are sited in the healthier tissue. In a very diseased thoracic aorta where the aneurysm is up to the left subclavian or left common carotid, a stent/graft needs to anchor adjacent to or above the left subclavian. The placement is critical because the graft section must not cover the left subclavian to allow for blood flow to the left subclavian through the open cells of the stent. If the stent/graft prosthesis is deployed such that the graft section covers the left subclavian, then a blockage of the left subclavian would be formed by the graft. If the graft section is deployed too far downstream, then occlusion of the aneurysm may not be achieved.
The accuracy of the placement of the stent/graft prosthesis is critical. If the stent/graft prosthesis is deployed too low into the diseased section, there is the potential for rupturing the wall, and the aneurysm is not occluded by graft. Also, in certain instances the stent/graft prosthesis may not properly anchor and the prosthesis may pose a potential blockage problem. If the stent/graft prosthesis is anchored too high it may block or cut off other critical arteries.
The design of the stent/graft deployment device directly affects the performance and accuracy of the delivery device in the fluid flow environment. For example, the inability to reposition the stent/graft upon deployment, and difficulties associated with maneuvering the device within the arteries. The design also attributes to the amount of retrograde pressure experienced from the blood flow during deployment. This retrograde pressure caused by the obstruction of blood flow causes the graft to twist, crumble and not properly unfold, and the stent may not anchor properly, move or shift during or after deployment.
Thus, there is a need in the art for a deployment device that accurately deploys a prosthesis, eliminating problems associated with concurrent deployment of a stent and graft, and blood flow obstruction, retrograde pressure. There is a need for a delivery device that offers the flexibility of post-deployment adjustments, and is least obstructive to the blood flow upon deployment.